The Gettier problem is considered a problem in modern epistemology arising from counter-examples to the definition of knowledge as justified true belief (JTB).
The problem owes its name to a three-page paper published in 1963, by Edmund Gettier, called "Is Justified True Belief Knowledge?", in which Gettier argues that this is not necessarily the case.
The Cow in the Field
Farmer Field is concerned about his prize cow, Daisy. In fact, he is so concerned that when his dairyman tells him that Daisy is in the field, happily grazing, he says he needs to know for certain. He doesn't want merely to have a 99 percent probability that Daisy is safe, he wants to be able to say that he knows Daisy is safe.
Farmer Field goes out to the field and standing by the gate sees in the distance, behind some trees, a white and black shape that he recognizes as his favorite cow. He goes back to the dairy and tells his friend that he knows Daisy is in the field.
Yet, at this point, does Farmer Field really know it?
The dairyman says he will check too, and goes to the field. There he finds Daisy, having a nap in a hollow, behind a bush, well out of sight of the gate. He also spots a large piece of black and white paper that has got caught in a tree?
Daisy is in the field, as Farmer Field thought.
But was he right to say that he knew she was?
The philosopher, Martin Cohen, who described this scenario originally, says that in this case the farmer:
believed the cow was safe;
had evidence that this was so (his belief was justified);
and it was true that his cow was safe.
However, we might still feel that the farmer did not really know it. Herein lies the core problem with the tripartite theory of knowledge.
Gettier's counterexamples
The Philosopher Gettier used counterexamples to argue that there are cases of beliefs that are both true and justified—therefore satisfying all three conditions for knowledge on the JTB account—but that do not appear to be genuine cases of knowledge. Gettier, therefore, argued that his counterexamples show that the JTB account of knowledge is problematic! — and that a different definition is needed to correctly track what we mean by "knowledge".
Case I
Smith has applied for a job, but, it is claimed, has a justified belief that "Jones will get the job". He also has a justified belief that "Jones has 10 coins in his pocket". Smith therefore concludes that "the man who will get the job has 10 coins in his pocket".
In fact, Jones does not get the job. Instead, Smith does. However, as it happens, Smith (unknowingly and by sheer chance) also had 10 coins in his pocket. So his belief that "the man who will get the job has 10 coins in his pocket" was justified and true. But it does not appear to be knowledge.
Case II
Smith has a justified belief that "Jones owns a Ford". Smith therefore (justifiably) concludes that "Jones owns a Ford, or Brown is in Barcelona", even though Smith has no knowledge whatsoever about the location of Brown.
In fact, Jones does not own a Ford, but by sheer coincidence, Brown really is in Barcelona. Again, Smith had a belief that was true and justified, but not knowledge.
False premises
In both of Gettier's actual examples, the justified true belief came about as the result of justified false beliefs, namely, that "Jones will get the job" (in case I), and that "Jones owns a Ford" (in case II). This led some early responses to Gettier to conclude that the definition of knowledge could be easily adjusted, so that knowledge was justified true belief that depends on no false premises.
More general Gettier-style problems
The "no false premises" (or "no false lemmas") solution which was proposed early in the discussion did not settle the matter, as more general Gettier-style problems were then constructed, in which the justified true belief does not seem to be the result of a chain of reasoning from a justified false belief.
For example:
After arranging to meet with Mark for help with homework, Luke arrives at the appointed time and place. Walking into Mark's office Luke clearly sees Mark at his desk; Luke immediately forms the belief 'Mark is in the room. He can help me with my logic homework'. Luke is justified in his belief; he clearly sees Mark at his desk. In fact, it's not Mark that Luke saw; it was a marvelous hologram, perfect in every respect, giving the appearance of Mark diligently grading papers at his desk. Nevertheless, Mark is in the room; he is crouched under his desk reading Frege. Luke's belief that Mark is in the room is true (he is in the room, under his desk) and justified (Mark's hologram is giving the appearance of Mark hard at work).
Again, it seems as though Luke does not "know" that Mark is in the room, even though it is claimed he has a justified true belief that Mark is in the room, but it's not nearly so clear that the perceptual belief that "Mark is in the room" was inferred from any premises at all, let alone any false ones, nor led to significant conclusions on its own; Luke didn't seem to be reasoning about anything; "Mark is in the room" seems to have been part of what he seemed to see.
To save the "no false lemmas" solution, one must logically say that Luke's inference from sensory data does not count as a justified belief unless he consciously or unconsciously considers the possibilities of deception and self-deception. A justified version of Luke's thought process, by that logic, might go like this:
That looks to me like Mark in the room.
I don't think any factor, right now, could deceive me on this point.
Therefore, I can safely ignore that possibility.
"Mark is in the room," (or, 'I can safely treat that as Mark.')
And the third step counts as a false premise. But by the previous argument, this suggests we have fewer justified beliefs than we think we do.
The problem owes its name to a three-page paper published in 1963, by Edmund Gettier, called "Is Justified True Belief Knowledge?", in which Gettier argues that this is not necessarily the case.
The Cow in the Field
Farmer Field is concerned about his prize cow, Daisy. In fact, he is so concerned that when his dairyman tells him that Daisy is in the field, happily grazing, he says he needs to know for certain. He doesn't want merely to have a 99 percent probability that Daisy is safe, he wants to be able to say that he knows Daisy is safe.
Farmer Field goes out to the field and standing by the gate sees in the distance, behind some trees, a white and black shape that he recognizes as his favorite cow. He goes back to the dairy and tells his friend that he knows Daisy is in the field.
Yet, at this point, does Farmer Field really know it?
The dairyman says he will check too, and goes to the field. There he finds Daisy, having a nap in a hollow, behind a bush, well out of sight of the gate. He also spots a large piece of black and white paper that has got caught in a tree?
Daisy is in the field, as Farmer Field thought.
But was he right to say that he knew she was?
The philosopher, Martin Cohen, who described this scenario originally, says that in this case the farmer:
However, we might still feel that the farmer did not really know it. Herein lies the core problem with the tripartite theory of knowledge.
Gettier's counterexamples
The Philosopher Gettier used counterexamples to argue that there are cases of beliefs that are both true and justified—therefore satisfying all three conditions for knowledge on the JTB account—but that do not appear to be genuine cases of knowledge. Gettier, therefore, argued that his counterexamples show that the JTB account of knowledge is problematic! — and that a different definition is needed to correctly track what we mean by "knowledge".
Case I
Smith has applied for a job, but, it is claimed, has a justified belief that "Jones will get the job". He also has a justified belief that "Jones has 10 coins in his pocket". Smith therefore concludes that "the man who will get the job has 10 coins in his pocket".In fact, Jones does not get the job. Instead, Smith does. However, as it happens, Smith (unknowingly and by sheer chance) also had 10 coins in his pocket. So his belief that "the man who will get the job has 10 coins in his pocket" was justified and true. But it does not appear to be knowledge.
Case II
Smith has a justified belief that "Jones owns a Ford". Smith therefore (justifiably) concludes that "Jones owns a Ford, or Brown is in Barcelona", even though Smith has no knowledge whatsoever about the location of Brown.In fact, Jones does not own a Ford, but by sheer coincidence, Brown really is in Barcelona. Again, Smith had a belief that was true and justified, but not knowledge.
False premises
In both of Gettier's actual examples, the justified true belief came about as the result of justified false beliefs, namely, that "Jones will get the job" (in case I), and that "Jones owns a Ford" (in case II). This led some early responses to Gettier to conclude that the definition of knowledge could be easily adjusted, so that knowledge was justified true belief that depends on no false premises.More general Gettier-style problems
The "no false premises" (or "no false lemmas") solution which was proposed early in the discussion did not settle the matter, as more general Gettier-style problems were then constructed, in which the justified true belief does not seem to be the result of a chain of reasoning from a justified false belief.For example:
After arranging to meet with Mark for help with homework, Luke arrives at the appointed time and place. Walking into Mark's office Luke clearly sees Mark at his desk; Luke immediately forms the belief 'Mark is in the room. He can help me with my logic homework'. Luke is justified in his belief; he clearly sees Mark at his desk. In fact, it's not Mark that Luke saw; it was a marvelous hologram, perfect in every respect, giving the appearance of Mark diligently grading papers at his desk. Nevertheless, Mark is in the room; he is crouched under his desk reading Frege. Luke's belief that Mark is in the room is true (he is in the room, under his desk) and justified (Mark's hologram is giving the appearance of Mark hard at work).
Again, it seems as though Luke does not "know" that Mark is in the room, even though it is claimed he has a justified true belief that Mark is in the room, but it's not nearly so clear that the perceptual belief that "Mark is in the room" was inferred from any premises at all, let alone any false ones, nor led to significant conclusions on its own; Luke didn't seem to be reasoning about anything; "Mark is in the room" seems to have been part of what he seemed to see.
To save the "no false lemmas" solution, one must logically say that Luke's inference from sensory data does not count as a justified belief unless he consciously or unconsciously considers the possibilities of deception and self-deception. A justified version of Luke's thought process, by that logic, might go like this:
And the third step counts as a false premise. But by the previous argument, this suggests we have fewer justified beliefs than we think we do.